The present invention relates to the fields of mechanical engineering, materials science, medical device technology and medicine. In particular, it relates to a high pressure vascular balloon catheter having a high degree of flexibility together with high resistance to rupture from internal pressure created by balloon inflation.
The following is presented for the purpose of understanding the context of the present invention and it is not to be construed and is not admitted to be prior art to this invention.
Catheters are being increasingly used to reach more and more remote locations in the body of a patient. When the target is a soft tissue site, the vascular system in the region often consists of vessels of very small diameter. The vessels also are often convoluted, making many sharp twist and bends. To navigate these small tortuous vessels requires a catheter having a correspondingly small outside diameter. The predominant method for achieving small diameters is to use catheters having very thin walls. However, as the walls of a catheter get thinner, they tend to lose their torsional and longitudinal rigidty. That is, while extraordinary flexibility is required to navigate the vessel of the vascular system, sufficient torsional rigidity must be maintained to permit steering of the catheter through the vessel and sufficient longitudinal rigidity must remain to allow the catheter to be advancexe2x80x94pushedxe2x80x94through the vessel. Furthermore, thin wall tubes have a tendency to crimp or kink when bent in a small radius. This can result in the binding of guidewires within the catheter thus frustrating further advancement of the catheter in the vessel which normally depends on prior advancement of a guidewire. A number of patents have been issued which purport to address torsional and longitudinal rigdity and kinking in thin-walled catheter tubes.
U.S. Pat. No. 4,676,229, to Krasnicki, et al. (1987), relates to a biopsy channel comprising a tubular substrate helically wound with a high strength wire filament, the winding being spaced sufficiently apart to provide regions between the windings into which a relatively softer elastomeric filler material can be interspersed. A top coating of a lubricious material covers the filler material. The resulting tubular structure is purportedly capable of tight radius bends without collapsing.
U.S. Pat. No. 4,981,478 to Evard, et al. (1991), relates to a vascular catheter having a tubular member of composite structure. The structure is comprised of a tubular substrate covered with a resin-impregnated fibrous material extending over a substantial part of the length of the tubular member. The fibers are epoxy-impregnated aramid or polyester multi-filament fibers. The fibers are described as being either spiral wound or braided around the tubular member. This structure purportedly affords a tubular member with longitudinal flexibility and diametric rigidity, i.e., kink-resistance. The fiber-reinforced tube may be placed within a second tube, e.g., a tube having a balloon-forming region at its distal end such as an angioplasty catheter.
U.S. Pat. No. 5,037,404, to Gold, et al. (1991) relates to a flexible catheter design in which the longitudinal flexibility and torsional rigidity are controllable along the length of the catheter shaft by encasing the shaft in a tubular braided wire sheath in which the angle between the crossing strands of the braid varies. The change in angle is stated to result in a change in the torsional and longitudinal rigidity of the catheter shaft.
U.S. Pat. No. 5,057,092 to Webster (1991), provides another means for controlling the flexibility of a catheter shaft, in this case to generally reduce rather than increase it. The ""092 patent discloses an elongated tubular body having an inner wall, a reinforcing braided tubular mesh interwoven with longitudinal warp strands surrounding the inner wall and an outer wall encasing the reinforcing structure between it and the inner wall. The modulus of elasticity of the longitudinal strands is lower than that of the helical mesh strands. This results, according to the patentee, in increased bending stiffness without a concomitant decrease in the resiliency of the catheter body.
U.S. Pat. No. 5,069,674, to Fearnot et al. (1991) describes a small diameter epidural catheter that is both flexible and kink-resistant. This is accomplished by expansion-fitting a wire coil inside a tubular sheath in which the ratio of the outside diameter of the wire coil to the cross-sectional diameter of the individual turns is within a range of 4 to 10. In this configuration, the wire coils are said to prevent the tubular sheath from rupturing or kinking when the catheter is flexed or bent.
U.S. Pat. No. 5,176,660, to Truckai (1993) discloses a catheter body consisting of at least one resilient tubular member in which the flexibility is controlled by wrapping the tubular layer in a sheath of helically-disposed crossing strands in which one of the strands is ribbon-like in cross-section and has a width that is 4 to 8 times its thickness. Other strands are circular in cross-section. A reinforcing filament generally parallel to the longitudinal axis of the tubular layer is also described. These various strand types and directional orientation is said to permit control of the torsional and longitudinal rigidity of the tubular member along the length of the catheter body.
U.S. Pat. No. 5,180,376, to Fischell (1993) describes an introducer sheath for an angioplasty or atherectomy catheter that consists of a thin, flat wire metal coil that is surrounded only on its exterior surface with a plastic coating. The claimed benefit of this design is to provide a sheath through which devices can be routed to a specific locus in a patient""s body wherein the sheath is as thin as possible but has the strength to resist buckling when being pushed through the femoral artery.
U.S. Pat. No. 6,152,912, to Jarlsen, et al. (2000) teaches a catheter suitable for accessing a tissue target in a patient""s body, the catheter having a reinforcing member wound within the catheter body to provide kink-resistance and controlled stiffness. The reinforcing member is comprises of a wire ribbon helically wound around an inner lubricious liner, the wire ribbon being helically back-wound over the top of the first winding on the more proximal portion of the assembly. The entire wire member is then over-coated with an outer layer of polymer.
The problem of achieving a small tube diameter while still having sufficient torsional and longitudinal control and kink resistance is compounded in cases where the use of a catheter comprised of more than one channel or tube is required such as in the treatment of atherosclerotic lesions in the arteries of the brain using a balloon catheter similar to, but necessarily much smaller than, that employed for percutaneous transluminal coronary angioplasty. Such a catheter is composed of two tubes, an outer tube that, at or near its distal end, is capable of being expanded to form a balloon-like structure and an inner tube through which a guide wire or other instrumentation may be passed. The annular space between the two tubes provides a channel through which liquids can be introduced and removed to inflate and deflate the balloon.
The general approach to accommodating the need for smaller outside diameter catheters is to reduce the size of guide wires and the wall thickness of both tubes making up a balloon catheter. However, there are limits to the extent to which these dimensional reductions can be taken. If the diameter of the guidewire is reduced too much, the guidewire will lose its ability to effectively transmit torsional and axial forces necessary to steer and advance the guide wire through tortuous vascular systems. If the diameter of the wire is maintained at a functional dimension, then the remaining way to reduce overall catheter size is to reduce the wall thickness of the tubular portions of the catheters. As noted above, this can result in loss of cross-sectional circularity of either or both the inside and outside tubes, resulting in crimping or kinking. If the inner tube kinks, then the guidewire will become bound within the tube""s lumen and can no longer be advanced through the vascular system. If the outer tube kinks, it may cause the inner to tube to close down and bind the guide wire or it may constrict, even close down, the annular space between the tubes making it impossible to expand and deflate the balloon structure.
The patents discussed above are directed to single tube catheters having controlled flexibility and kink resistance to permit traversing small vascular channels. However, none of the aforementioned designs provides a balloon catheter structure combining a very thin overall cross-section with controlled flexibility, kink resistance and the structural strength to withstand the high pressures created during the inflation of the balloon portion of the catheter. The present invention provides such a catheter.
Thus, in one aspect, the present invention relates to a high-pressure balloon catheter, comprising:
a first flexible elongate tubular member having a proximal end and a distal end, the first member having an outer surface and an inner surface that describes a lumen; a second flexible elongate tubular member having a proximal end and a distal end, the second elongate member being disposed within the lumen of the first elongate tubular member and extending distally beyond the distal end of the first elongate member, the second member having an inner surface describing a lumen and an outer surface describing an outer diameter that is less than an inner diameter of the first elongate member such that an annular lumen is formed between the first and second elongate members;
an inflatable balloon-forming structure having a proximal end and a distal end, the structure being sealably coupled at its proximal end to the distal end of the first elongated member and at it""s distal end to the distal end of the second elongate member;
a first reinforcing member disposed between the inner and outer surfaces of the flexible portion of the first elongate member, the first reinforcing member comprising a plurality of strands, each strand having a width and a thickness; and,
a second reinforcing member disposed between the inner and outer surfaces of the second flexible elongate member.
In another aspect, this invention relates to the above high pressure balloon catheter in which the first reinforcing member is a first braided reinforcing member.
It is also an aspect of this invention that, when the first reinforcing member is a braided reinforcing member, each of the strands of the braided reinforcing member have a width of from about 0.002 to about 0.004 inches.
In a further aspect, this invention relates to the above high pressure balloon catheter wherein each strand of the first braided reinforcing member has a thickness of from about 0.0004 to about 0.00075 inches.
Each strand of the first braided reinforcing member has a width of about 0.003 inches and a thickness of about 0.0005 inches in yet another aspect of this invention.
It is an aspect of this invention that the first reinforcing member is selected from the group consisting of a metal and a high tensile strength fiber.
The metal of which the first reinforcing member is constructed is selected from the group consisting of nitinol and stainless steel in a still further aspect of this invention.
The high tensile strength fiber of which the first reinforcing member is constructed is selected from the group consisting of aramid, vertran, liquid crystal polymer and carbon fiber in another aspect of this invention.
It is an aspect of this invention that the proximal end of the balloon-forming structure is sealably coupled to the distal end of the first flexible elongate member by a butt weld.
It is an aspect of this invention that, in the above butt-welded balloon forming structure, the first reinforcing member extends distally over the butt weld.
In yet another aspect of this invention, the first reinforcing member extends completely over the balloon-forming member to the distal end thereof.
The balloon-forming member has an inner surface and an outer surface, the first reinforcing member being disposed between the inner and outer surfaces from the proximal end of the balloon-forming structure to the distal end of the balloon-forming structure in a further aspect of this invention.
It is an aspect of this invention that the second reinforcing member extends from a point distal to the proximal end of the first reinforcing member to a point distal to the proximate end of the balloon-forming structure.
The second reinforcing member comprises a second braided reinforcing member in another aspect of this invention.
The second braided reinforcing member comprises a plurality of strands, each having a width and a thickness in an aspect of this invention.
Each strand of the second braided reinforcing member has a width of from about 0.002 to about 0.004 inches in a further aspect of this invention.
Each strand of the second braided reinforcing member has a thickness of from about 0.0004 to about 0.00075 inches in an aspect of this invention.
Each strand of the second braided reinforcing member has a width of about 0.003 inches and a thickness of about 0.0005 inches in a still further aspect of this invention.
It is an aspect of this invention that the second reinforcing member is selected from the group consisting of a metal and a high tensile strength fiber.
The metal from which the second reinforcing member is formed is selected from the group consisting of nitinol and stainless steel in an aspect of this invention.
The high tensile strength fiber from which the second reinforcing member is formed is selected from the group consisting of aramid, vertran, liquid crystal polymer and carbon fiber is an aspect of this invention.
In another aspect of this invention, a channel is located at the distal end of the balloon-forming structure where the structure is coupled to the distal end of the second elongated flexible member, the channel operatively coupling the interior of the balloon-forming structure with the external environment.
A further aspect of this invention is a high-pressure balloon catheter that, in addition to having the first and second reinforcing members described above, also comprises a balloon-forming structure having an inner and an outer surface wherein a third reinforcing member is disposed between the inner and outer surfaces from the distal end of the balloon-forming structure to a point proximal to the proximal end of the balloon-forming structure such that, when the proximal end of the balloon-forming structure is coupled to the distal end of the first elongate member, the third reinforcing member extends proximally over the coupling.